Data gathered during the last year suggests that 5 alpha- and 5 beta-DHT stimulate erythropoiesis in exhypoxic polycythemic mice in a specific manner that does not involve the androgen receptor found in secondary sex tissue, kidney, brain and salivary gland. A major emphasis of the work to be done during the coming year will be to begin to elucidate the mechanism by which these steroids act at the level of the stem cell. In vivo studies using 3H-steroids will be done to characterize the subcellular localization of the active steroid. In vitro studies will focus on characterizing the mechanism by which these steroids act at the subcellular level. Characterization of the metabolism of erythropoietic steroids will be continued in both intact and tissue minces of normal and anemic mice.